Art of effecting heat exchange



Dec. 2, 1930.

w. D. LA MONT ET AL ,783,7 4

ART OF EFFECTING HEAT EXCHANGE Filed 1926 Sheets-Sheet l lNVENTOR Wan Pk 0006146 u/fa/vr a Patentecl Dec. 2, 1930 UNITED STATES WALTER DOUGLAS LA MOR'T, OF LARCHMONT, NEW YORK, AND ALFRED F. ERNST, OF PASSAIC, NEW JERSEY, ASSIGNORS TO LA MONT CORPORATION, OF NEW YORK, N. Y.,

A CORPORATION OF NEW YORK v AR'I. or EFFECTING HEAT EXCHANGE Application filed October 7, 1926. Serial No. 140,099.

the invention is so to direct and control this heat exchange in accordance with the physical laws of heat and the physical characteristics of the different substances between which the exchange is to take place as to obtain substantially the practicable maximum of efliciency of heat transfer, or in other words so to direct and control this heat ex change that within the limits of practicability substantially a maximum of heat transfer will take place from one substance to another during the time that the substances are in heatexchanging relation to each other and that the rate of heat transfer will likewise be increased.

Although the invention is herein particularly illustrated in its application to the generation of steam by the transfer of heat from heated gases to water, it will be understood that the invention is not restricted in its utility or applicability to the uses or to the embodiments herein illustrated and described,

but that it has quite general utility in the one or more or all of these modes of transfer. The present invention. while intended to take" advantage of the exchange of heat byconduction and by radiation, at least to the same extent as by the methods and with the apparatus heretofore employed, relates particularly to the transfer of heat somewhat after the manner that heat transfer is accomplished by convectloman ob ect of the Invention being to utilize convection, or bodily translation relative to the stream movement of the particles of at least one of the substances to or from which heat is to be transferred, in such man-- ner and under such control as to determine to a substantial degree the speed, direction and amplitude of the heat-transferring movements and contacts of the particles of the heat-conveying vehicle or fluid and thereby obtain substantially the practicable maximum of heat-transferring efficiency while the heatconveyingvehicle and the substance to or from which heat is to be transferred remain in heat-exchanging proximity to each other.

The invention relates particularly to ob taining the practicable maximum of heatexchanging efliciency when the heat conveying vehicle is a fluid. When a fluid, whether liquid or gas, is used as the heat conveying vehicle, it will be apparent that in order to insure as great heat transfer as possible between the fluid and the substance to be heated or cooled, as many contacts as possible of diflerent particles of the fluid with the substance to be heated or cooled must be effected, since conduction from the heated particles of the fluid to the particles of the fluid which are not heated is comparatively little,

of a heat conveying fluid in heat-exchanging.

relation to the substance to be heated or cooled as to insure, while in suchheat-exchanging relation, the maximum of heat transferring contacts.

Leaving out of account for the moment any movement of the substances to be heated or cooled, the invention aims, in the first place, to move the vehicle from or to which heat is to be transferred, whether gas or liquid, at such a velocity with relation to the substance to be heated or cooled, and also in such relationto the exposed surface of such substance, that advantage may be taken of the phenomenon called turbulence which occurs when a fluid is moved at a velocity appreciably higher than that which produces uniform rectilinear motion of the particles of the fluid. This velocity at which a chaiige from rectilinear motion of the particles of the moving fluid occurs has commonly been called the critical velocity of the fluid. It is the velocity which is obtained by labora tory methods in experiments to determine that speed of flow at which a particle of fluid deviates from its rectilinear motion,

The present invention takes advantage of this critical velocity of fluids by so controllin the velocity of the fluid utilized to effect t e heat transfer, whether to or from this fluid, that its velocity will be at or above the critical velocity of this fluid, thereby producing an appreciable turbulent motion of the particles of the fluid in directions at angles to the direction of flow of the fluid.

The invention aims further so to control this velocity that, where desirable, substantially the maximum displacement of the particles of the fluid laterally with respect to the direction of flow may be obtained. Such a velocity may, for convenience, be termed maximum ranging velocity where the term ranging is used to define the lateral movemum ranging motion, the invention further.

ments of the particles with respect to the direction of flow of the fluid.

In addition to controllin the velocity of the fluid used for heat trans er, whether to or from this fluid, so as to obtain an effective rangin movement of the particles of the fluid, or the purposes in view, whether or not this be the velocity producing the maxiaims to concentrate, within the cross-section of the flow of the fluid moving atthe desired ranging velocity a plurality ofportions of the substance to be heated or cooled, orthe heat-exchan ing surface in such way that the heat-exc anging sur ace has its area extended principally in the direction of the of the invention is so to subdivide the substance to be heated or cooled, or the heatexchanging surface, that thedistances apart and the locations of its respective portions will be within the limits of the ranging action of the particles of the fluid, and preferably so t arrange these portions that there will be a mat-exchanging surface within the range of any particle no matter what the transverse direction of its ranging movement.

Not only is it important, for ultimate economy and efficiency, to rovide heat-exchangin or contacting sur aces within the range 0% movement of the particles of the heat conveying fluid and so to determine the velocity of the fluid as to obtain the desired effective ranging movement, but it is also important that these heat-cex'changingisurfaces be extended along the path of move.- ment of the heat conveying fluid a sufficient distance to insure the desired total heat transfer. By so confining the fluid stream as to obtain an initial velocity of the heat conveying fluid approximating its maximum effective ranging velocity andalso simultaneously so determining such a spacing of the different portions of the heat-exchanging surface within the stream that the distance from any one portion to each of several adjacent portions will not be greater than the limits of the ranging action of the particles of the fluid, it will be seen that the desired or substantially the maximum amount of heat per unit of length of travel of the fluid or per unit of time will be transferred, since the opportunity for the molecules or the particles of fluid to transmit their vibratory motion to the substance to be heated or to the heat-exchanging surface will be substantially a maximum. It will further be seen thatby extending the heat-exchanging surface along the path of travel of the heating fluid the desired total transfer of heat may be effected.

To effect such desired total transfer most efficiently, however, that is, with a minimum of apparatus and within a minimum of time,

involves other considerations than mere extent of the heating surface along the path of travel of the fluid, even when such heating surface is so sub-divided at the point where the heating fluid first comes into contact with it as to insure the desired exposure of the surface tothe ranging action of theparticles of the fluid at that point. As a result of the transfer of the heat of the heat conveying fluid to the heat-exchanging surface or the transfer of heat to the fluid, there is a cooling or heating of the fluid which effects a change in its density and therefore in the volume of the same weight of the moving fluid. When the fluid is employed as a heating fluid, if the spacing of the heat-exchanging surfaces throughout the path of travel of the fluid over said surfaces remains the same and provides the same cross-sectional area of the stream, not only will the increase in density due to cooling, with the resultant reduction in volume, affect the velocity of the fluid overthe heat-exchanging surfaces in the later parts of its path of travel, but such reduction in volume and velocity will, within certain limits, also effect a reduction in the ranging motion of the particles of the fluid. and thus, with uniform spacing of the heating surfaces throughout the path of travel of the heating fluid thereover, in most cases-reduce the contacts and the rate of heat exchange in the laterparts of the path of travel.

Afurther important object of the present invention, therefore, is so to v ry the spacing ofthe surfaces which confihe and determine the velocity ofthe fluid stream that an efl'ective ranging velocity may'be maintained substantially throu bout the travel of the fluid over such sur aces and so to space the heat-exchanging surfaces that each will be wlthm the ranging action of the particles of i the fluid throughout the travel ofthe fluid of heat transfer.

thereover. In the case of a heating fluid, therefore, both the stream confining and the heat-exchanging surfaces will preferably gradually approach each other along the later parts of the path of movement of the fluid thereover, suclr narrowing of the distances between the different portions of the heatexchanging surfaces being preferably so determined that, while avoiding excessive draft'loss, an effective ranging velocity of the fluid will nevertheless be maintained throughout its travel over the heat-exchanging surfaces and that'these surfaces will be so located within the limits of the ranging motion produced by the velocity at each point along the path of travel of the fluid that an efficient heat-exchanging bombardment of the surfaces by the particles of the fluid will take place throughout such travel.

It will be understood, of course, that other factors than the mere confining of the fluid stream so as to obtain and maintain a maxi mum ranging velocity enter into the obtaining of the practicable maximum of efficiency As above suggested, with uniform spacing of the heat-exchanging surfaces and a constant cross-sectional area of the fluid stream, reduction in volume due to loss of heat effects both a reduction in velocity and a reduction in ranging movement of the particles of the fluids. If, however, the spacing of the surfaces which confine and which are located in the fluid stream be so 're'duced'as to compensate for this reduction involume and thus maintain a velocity which will maintain the maximum ranging motion, it is probable that, in some cases, the additional power required to force the fluid between the closely ,spaced sin-faces would more than offset the increased efficiency of heat exchange, particularly where the heat ex-' change is being effected for the purposes of power production. It will thus )0 seen that there is an advantage in the outer"reaches of the path of the fluid travel in effecting a compromise between that spacing of the stream confining surfaces which would produce the maximum ranging velocity of the gases and a spacing which, while not causing a marked draft loss, would, nevertheless, wit-h the reduced velocity produced by such spacing, be

tain the maximum ranging velocity nevertheless effects an acceleration of heat exchange (by reason of the marked increase in the heat-exchanging contacts between the surfaces and the particles of the fluid) over a velocity produced by a spacing of the streanr confining and heat-exchanging surfaces which while avoiding excessive draft loss,

would, nevertheless reduce the velocity so mu ch that the heat-exchanging surfaces would be spaced beyond the normal amplitude of ranging movement of the particles of the fluid for that velocity.

In other words, the inventionaims to maintain an effective ranging velocity of the heatconveying fluid by so restricting, at successive points along its path of flow, the crosssectional area of the fluid stream flowing over the' heat-exchanging surfaces distributed throughout the stream, and so spacing these heat-exchanging surfaces from each other in the stream that while the pitch and amplitude of the ranging action of the particles of the fluid resulting from the stream velocity produced by the restricted cross-sectional area is such as to insure an effective number of contacts of the particles of the heating fluid with the heat-exchanging surfaces for the particular spacing of the heat-exchanging surfaces, nevertheless the resistance offered by the stream-confining and heat-exchanging surfaces to the flow of the fluid will not be such as to cause an excessive draft lioss or uneconomically to impede the fluid For convenience of illustration, the invention .in one of its forms is shown as embodied in a steam generator of the general type disclosed in U. S. Letters Patent No. 1,545,668, to WV. D. La Mont, dated July 14, 1925. Steam generators of the type disclosed in the Letters Patent ustidentitied, as now usually constructed, comprise relatively long thinwalled tubes of small diameter arranged substantially upright in closely spaced relation to each other so that the heating gases passing up through the spaces between the tubes must come into heat-exchanging contact with the tubes at many points throughout their travel. travels downwardly through the tubes in the form of' films on the inner walls thereof so that it moves in counterflow relation to the heating gases, and the tubes are preferably of such length that when the gases pass out 7;;

of heat-exchanging relationship thereto they have had their temperature lowered at least. to the temperature of the steam issuing at the lower ends of the tubes or even lower, so that there is a zero or even a sub-z ro heat head where the incoming water first comes into heat-exchanging relationship to the gases.

- As the gases travel up the tubes and heat is extracted therefrom, they contract somewhat in volume, which results, in the case The water to be heated preferably tubes will be within the limits of the ranging motion, for this velocity, of substantially every particle of the gas throughout the travel of the gas along the tubes, thereby insuring contact of substantially every particle of the gas with the heat-exchanging surface of the tube group at a plurality of points during its travel along the tubes.

One of the objects of the present invention is so to confine the gas or fluid stream and so to distribute the tubes of the generator in this stream that in the first place astream velocitywill be obtained which will secure the desired ranging motion of the particles of the gas or other heating fluid, and that, in the second place, there will be located in the stream tube surfaces so spaced with respect to each other as to present a tube surface within the limits of the lateral range of movement of substantially every particle of gas at substantially every point along the path of travel thereof.

Theinvention aims particularly to maintain the efficiency of heat transfer throughout the travel of the gases over the generating tubes and preferably not only to determine such cross-sectional area of the gas stream and such a distribution of the tubes in the gas stream as will produce substantially the practicable maximum of efliciency of heat transfer where the gas first comes into heat-exchanging relationship to the tubes, but also preferably so to vary the cross'sectional area of the gas stream and so to vary the distribution of the tubes in the stream, or their relative spacing, that as the gas or other heating fluid contracts in volume due to loss of heat, a velocity of stream flow will be maintained and a spacing of the tubes with respect to each other will be provided which will maintain a high heat-transferring efficiency throughout the travel of the gas over the tubes while preferably avoiding excessive or uneconomical draft loss.

Other objects and important features of the invention will appear from the following description and claims when considered in connection with the accompanying drawlngs, in which Fig. 1 is a diagrammatic section illustrating the shape of a fluid-confining passage required to maintain a maximum ranging velocity of flow of the fluid therethrough under conditions in which the fluid either takes up or gives off heat, the diagram illustrating the shape of such a fluid passage when the rate of heat transfer follows the law of heat differential and the flow-impelling pressure is substantially uniform. This figure also illustrates in dotted lines the normal amplitude and pitch of the ranging motion of a particle of the fluid at this constant velocity; 1

Fig. 2 is a view similar to Fig. 1, showing the possible actual path of travel of the ranging particle owing to the fact that the normal amplitude 'of its ranging motion produced by the uniform velocity is greater than the width of the passage required to roduce the velocity whereby the particle stri es the side wall of the passage before completing its lateral swing;

Fi 3 is a view illustrating a modified shaping of the fluid passage, which while not.

suited to the maintenance of a uniform velocity of the fluid through the passage, nevertheless will maintain at all times such a velocity that the ranging motion produced thereby will have an amplitude and pitch suited to the dimensions of the passage;

Fig. 4 is a diagrammatic illustration of the possible practicable boundaries of effective ranging velocities;

Fig. 5 is a view of a steam generator of the general type disclosed in Letters Patent No. 1,545,668, hereinabove referred to, having its heat-exchanging surfaces and gas passages so constructed and arranged as to take advantage of the improvements in the art of heat exchange which are the subject-matv ter of the present invention;

Fig. 6 is a horizontal section through the heat chamber and steam generating tubes, on the line 6-6 of Fig. 5; and

Fig. 7 is a similar section on the line 7-7 of Fig. 5.

As hereinabove suggested, the invention is directed to taking advanta e of certain phenomena resulting from the movement of fluids through passages at velocities beyond those at which the particles of the fluid maintain a substantially rectilinear direction of movement, by so confining the fluid to or from which heat is to be transferred that the velocity of the fluid thus confined and subjected to its flow-impelling pressure will produce an effective ranging action of the particles of the fluid, and so exposing the heat-exchanging surface to the fluid that there will be a portion of the surface within the rangerof substantially every particle of the fluid at substantiall every point along the path of flow of the uid thereover.

If we assume that the heat-conveying vehicle is 'a vapor or gas and that as it travels over the heat-exchanging surface it loses or takes up heat at a rate, determined by its drop or rise in heat head'a-t difl'erentpoints along the path of travel, we then have a curve these walls also providing heat-exchanging surfaces. The reduction in the cross-sectional area of the passage toward the right in Fig. 1 corresponds tothe reduction in volume of a gas having a' temperature drop varying in rate with its loss of heat head as it moves to the right along this passage. It will thus be seen that if there is a constant flow-im pelling pressure on the gas the velocity of the gas will remain substantially uniform as it travels through the passage.

Leaving out of consideration any variation in the amplitude of the lateral ranging movement of the particle of the gas which might result from an increase in the density thereof, it will be apparent that'if this constant velocity of the gas flowing through the passage bounded by thewalls 2 and 4 is the maximum. ranging velocity of the gas and that if at the point where the gas enters the passage the walls 2 and 4 are so spaced that a particle-of gas following the dotted line path 6 would, as it struck the wall 2,

.be substantially at the extremity of its movement to one side of the center of its line of motion; in other words, if the Walls 2 and 4 at this point are spaced a distance apart equal substantially to the amplitude of the ranging motion of the particles of the gas at the maximum ranging velocity, then, with the maintenance of this velocity throughout the travel of the gas through the passage, this particle would still tend to follow the sinuous dotted path of movement shown in Fig. 1. Because of the confining walls, however. it. would not be able to follow this'path and itis quite probable that its path of movement would be more nearly'like that of the solid line 8 in Fig. 2.. v

It will thus be seen that by so spacing the heat-exchanging surfaces as to form a gas passage that will maintain the maximum ,ranging velocity of the gas throughout its .travel over the heat-exchanging surfaces we obtain in the outer reaches of the travel of the gas a spacing of these surfaces closer than required for effective contact of the particles of the gas therewith. Moreover, with the relatively long gas passages essential for substantial total heat transfer, that is, substantial reduction of the heat head to zero, it is probable in most cases that the reduction in the cross-sectional area of the passage necessary to maintain the maximum ranging velocity for the outer reaches of the travel of the heating gas would be such as seriously to interfere with the draft. In other words, the

draft loss of the increased "frictional resistance to the movement of the gases would be so great that theadd'itional power required to overcome this draft loss might more than olfset the increased efficiency of heat exchange, particularly if 4 the purpose of the heat exchange. be the production of power.

One of the objects of the present invention, therefore, is so to shape the fluid passages that the fluid in traveling over the heat-exchanging surfaces, while not necessarily having its maximum ranging velocity at all points throughout its path of travel, will yet, at every point, have a ranging velocity suited to the spacing at that point of the heat-exchanging surfaces in the fluid stream. For exam: ple, in Fig. 3 is illustrated a modification of the passage shown in Figs. .1 and 2, in which, inorder to avoid excessive draft loss, the fluid or gas passage has not been so restricted in the outer reaches of the gas travel as to maintain the initial and usually the maximum ranging velocity of thegas, but has been so restricted that, while avoiding excessive draft losses, it will yet maintain a velocity some what lower than the initial velocity, which will nevertheless produce an effectiveturbulence or ranging motion of the particles of the fluid, a substantially limiting condition being that shown in Fig. 3, in which the sinuous path of travel of a particle of the fluid is shown as having its lateral limits substantially at the walls of thetube throughout its travel, such result being obtained by so shaping the passage that the velocity of fluid travel produced thereby as the fluidloses heat and volume, will cause a gradual reduction in the pitch andin the amplitude of the ranging motion at successive points along its path whereby/the amplitude at each point is sub -stantially equivalent to the transverse dimension of the passage at that point.

It will be apparent, as illustrated in Fig. 4,

that the fluid velocity producing the ideal condition of rangmg motion is not necessarily the maximum velocity obtainable, al-

though from experiments heretofore conducted it has been ascertained that heat transfer within certain limits is dependent upon the velocity of movement of the heat-conveying fluid over the heat-transferring surface. From an examination of Fig. 4, however, it will-be seen that above the critical velocity there will be a velocity that will give the maximum amplitude of ranging mot-ion, this being illustrated by the sinuous path a of the movement of a particle of the fluid at this velocity. It will. further be apparent that as the velocity increases beyond this maximum ranging velocity the pitch will be greater butthe amplitude less and that therefore'within a confined passage of definite dimensions the number of contacts of the particles with the heat-exchanging surface will be less; This is shown by the sinuous line b of the path of travel of the particle at a velocity above the ity, both the pitch and maximum ranging velocity. With a velocity somewhat below the maximum ranging velocthe amplitude of the ranging motion will be less than that of the maximum ranging velocity, as shown by the sinuous line 0 in Fig. 4. The ideal spacing of the surfaces which confine the fluid stream, or of the heat-exchanging surfaces within a fluid stream, is therefore such that when the fluid stream is moving at its maximum ranging velocity these surfaces will be spaced apart distances at or slightly within the amplitude of ranging motion of the particles of the fluid at that velocity. By this condit on may be obtained substantially the maximum of surface contact and therefore of heat transfer.

As -above pointed out, however, if we so arrange the heat-exchanging surfaces that they shape a passage for a heat-conveying gas which will maintain the initial maximum ranging velocity of the gas throughout its travel through the passage, we then meet the condition illustrated in Fig. 1, in which the heat-exchanging surfaces are so spaced apart as not to obtain the maximum benefit of the amplitude of ranging motion produced by this maximum ranging velocity. Moreover, with relatively long gas passages, the choking action in the outer reaches of the gas travel due to the restriction of the passage necessary to maintain the maximum ranging velocity might require the application of art1- ficial draft-producing means, utilizing an amount of power more than equal to the ncreased efficiency of heat exchange resulting from this maintenance of the initial maximum ranging velocity through those parts of the gas passage.

It will be understood that thereare two surface factors entering into the efliciency of heat exchange, one being the stream confinin factor and the other the heat-exchanging actor. It will be apparent thatui a relatively lar e gas passage the confining function may e effected by having the surfaces so located as to secure the desired velocity of stream flow without their; necessarily being so located as heat-exchanging surfaces that they are within the amplitude of the rangin motion of the particles of the fluid produced by that velocity. It 15 therefore important not only so to locate the surfaces for confining the stream that they will produce the desired ranging velocity, but

. also so to distribute the surfaces for heatexchanging purposes throughout this stream that a portion of these surfaces will be within the range of motion of substantially every particle of the. fluid at substantially every point along its path of travel.

- case of a heating fluid transferring its heat to the heat-exchanging surfaces, involves not only a restriction of the fluid passage to This, in the maintain an effective ranging velocity, as the fluid loses heat in its travel along this passage but also such a variation in the spacing of the heat-exchanging surfaces as will maintain the initial condition of a portion of the heat-exchanging surface located within the limits of the range of movement of substantially every particle atsubstantially' every point along the path of travel.

As above suggested in connection with the discussion of Figs. 1 to 3, in the practical application ofthe invention, for example, to the passages for heat-conveying gases between heat-exchanging surfaces, a compromise between ashaping of the gas passage and a location of the heat-exchanging-surfaces therein such that the maximum ranging velocity of the gases would theoretically be maintained, that is, a proportioning of the gas passages to the Variation in volume or in density of the heating gas with a resultant amplitude of ranging motion of the particles of the gas above that which can be efliciently utilized in the narrowed gas passage, on the one hand, and the maintenance of a uniform gas passage with the resultant lowering of the velocity of travel of the gas in the outer reaches of its travel and its attendant reduction of the ranging motion of the particles of the gas below an efiicient heat-exchanging level, on the other hand, and a compromise presents the best inter-relationship of the heat-exchanging and fluid passage defining surfaces for efficient and economical heat exchange. Such a compromise is illustrated diagrammatically in Fig. 3 in which the shaping of the heat-conveying gas passage has been sq chosen that while it will not maintain the initial ranging velocity of the gas, whether maximum or otherwise, as the gas loses heat it nevertheless will maintain an effective ranging velocity. Moreover it avoids excessive draft loss and presents the heat-exchanging surfaces at all points within the limits of the rangin motion of the particles of the gas produce by the velocities at the respective points.

In previous attempts to solve the problem of efficient heat exchange, particularly in steam generating apparatus, alleged relationships between hydraulic mean depth and length of gas travel have been worked out. A comparison of the applications of such forinulae to tubes of different diameters will show that such formulae do not take into consideration the equally important factor of turbulence or ranging motion of the particles of the gas at given velocities and that a heat-exchanging structure answering the terms of such formulae mightbe constructed in which the efficiency of heat exchange would be 'verymuch less than that in which provision is made in the spacing of the heat-exchanging surfaces for utilizing to its fullest invention, the dimensions and the spacing 1 of the heat exchange surfaces, or tubes, is

such that the heat exchange surfaces have an area of at least, 12 square feet per cubic foot of total volume of the passage, including the volume of the tubes, and that, if the gas is' travelingat a rate above the critical velocity when it enters the passage, a marked turbulence will be maintained in the gas throughout its entire travel therein. It is however not necessary that the initial gas velocity be maintained, but this may be permitted to decrease, as explained, provided it be kept high enough to maintain the turbulence.

Having shown ina general way how the control of the path of movement of a particle of a heat-conveying fluid is so effected as to obtain a great number of contacts of the particle with the heat-exchanging surface and therefore a high rate of heat-exchanging etficiency, the invention will now be described in connection with its application to the generation of steam. .As hereinabove pointed out, thesteam generator illustrated in Figs. 5, 6 and 7 is of the general type disclosed in the Letters Patent to Walter Douglas La Mont, No. 1,545,668, hereinabove identified. This generator usually comprises a comparatively large number of relatively "long, thin-walled, closely spaced generating tubes 12 of small diameter; for example, tubes of a length of 25 feet, an external diameter of inch, and" an internal diameter of inch. These tubes 12 in the illustrated construction are arranged in banks or trays from 5 to 13 tubes in each,

tray, with distributing headers 14 at their upper ends and collecting headers 16 at their lower ends, the water being delivered to the tubes from the distributing headers 14 in a manner as set forth in the patent to Walter Douglas La Mont, No. 1,545 668 and inquan-' tity less than suflicient to fill the tubes but greater than the generating capacity thereof, so that the water travels down the inner surfaces of the tubes in the form of films on these surfaces, both steam and water,being delivered to the headers 16 from the lower ends of the tubes and received into a common collecting pipe 18 by which the water and steam are conducted into a tank 20 in whigh a separation of the steam and water takes place,- the steam being conducted away through a steam main 22 and the water being returned through pipe 24, pump 26, plpe 28, strainers 30, pipe 32, to the manifold 34 connected to the headers 14. Thisgeneral conin a substantially vertical stack-like heat chamber 36 in a casing 38, the casing 38 being ends is about g lined with insulating material 40 surrounding and defining the shape of the heat chamber 36. The heat from any suitable source as, for example, waste heat from a water gas generating set may be conducted into the heat chamber through the heat inlet 42 shown as arranged obliquely to the vertical axis of theheat chamber and so located as to directthe heat into the heat chamber preferably at a point above the collecting headers 16.

In shaping the heat chamber 36, and in spacing'the steam generating tubes 12 therein, regard is had to the laws of heat exchange hereinabove discussed, and a compromise is effected between a shaping of the heat chamber 36, coupled with a distribution of the generating tubes 12 throughout the chamber, which would maintain a constant velocity of flow of the heating gases through the chamber and between the tubes, and a uniform shaping coupled with spacing of the tubes which would result in such a loss of velocity of flow of the gases at the upper ends of the tubes as'would seriously reduce their turbulence and the lateral motion of the particles thereof. It will be noted that the inner surfaces 44 of the insulating walls 40 of the heat chamber are curved substantially in accordance with the curvature of the gas passage illustrated in Fig. 3 of the drawings and that the spacing of the tubes 12 in the heat chamber 36 is varied to correspond with the variation in the cross-sectional area of the chamber.

whereby the gas passages between the tubes 12 vary in their cross-sectional dimensions 111 substantially the same manner as the heat chamber 36 varies in its cross-sectional dimenhaving tubes 12 about 25' 6" long and outside diameter, the spacing between the outer surfaces of the tubes at their lower and at their upper ends is lVhen heat for the generator-is provided by the blow gases during the blow of an ordinary water gas generating set, this spacing gives a velocity of about 5380 feet per minute. The velocity of the gases as they the tubes is 3670 feet per minute, theheatexchanging eificiencyo the generator is very high, the stack temperature being at or below the steam temperature, and the draft loss is very low.

From an examination of Figs. 5,6 and 7, it will be seen that the gas passages between the tubes correspond substantially to the illustra tion in Fig. 3, the tubes approaching each other at their upper ends so that while they are not necessarily spaced to maintain the initial velocity of the gases, they will still lnaintain marked turbulence and an effective ranging velocity and present heat-exchangingsurfaces within the range of the particles of the gas at this velocity.

emerge from the spaces at the upper ends of the surfaces for eflicient heat exchange, a

wider spacing of the surfaces with the resultant lowering of the velocity of the gases probably producing an amplitude of ranging motion too low to insure elfective contact of the particles of the gas with the heat-exchanging surfaces. The ideal spacing of the heat-exchanging surfaces and shaping of the gas passages to meet the average conditions is probably somewhat between that illustrated in Fig. 3 and that illustrated in Fig. 1, such a spacing making provision for utilization of a possible kinetic energy factor present in the higher ranging velocities. It is substantially such an intermediate shaping of the gas passages and spacing of the heat-exchanging surfaces that is illustrated and described herein as being embodied in a steam generator of the La Mont type.

It will be noted that in this embodiment of the invention andembodiment of means for carrying out the novel process'of the present invention, the mean hydraulicv depth where the gases enter. the generating space is comparatively low and is a mean hydraulic depth in every sense of the term. In other words, the tubes are so distributed through the heat chamber 36 that the cross-sectional area of the gases surrounding each tube is substantially the same. Moreover, the mean hydraulic depth at the upper end of the tubes is still lower and the tubes here, as at the lower ends and at all points along their length, are so distributed throughout the cross-sectional area of the heat chamber 36 that the crosssectional area of the gases surrounding each tube is substantially the same.

In calculating the cross-sectional area of the heat chamber 36 for a generator in which there are 1225 tubes and an initial velocity of 5380 feet per minute, the tuhesbeing each in outside diameter, we have the following computations, the net free area for the initial velocity of 5380 feet bein'g 10.68 sq. ft. The area of the cross-section of each tube will be .307". The total area in square feet occupied by the tubes at the lower end of the chamber will then be The total area of the cross-section of the chamber is then 2.62 sq. ft.

sq. ft. total area cross-section.

I \Vith a shaping of the heat chamber to give an sq. ft. This added to the total area in crosssection of the 1225 tubes, gives the following:

8. 17 sq. ft. 2. 62 10. 79 sq. ft. total area at the upper end of the chamber.

In order to get the diameter of the chamber at each end, the following equations may be used, letting d-eq ual the diameter:

igziihd d= 4 4.12 diameter at the lower end of the chamg 4=d l= =3.71 diglpeter o! the chamber at its upper If we were to maintain a uniform velocity the reduction in volume with the cooling off being in proportion to the absolute temperature of the gases,the total area of the crosssection of the heat chamber at its upper end would work out as follows:

Taking the initial temperature of the gases as found in actual practice, with a generator of the design herein shown, 1200 F and add to this the differential to give the absolute temperature, 460, the absolute initial temadding to this the total area ofithe tube crosssections,

The diameter at the upper end of the heat chamber for the uniform velocity, 3.23, is therefore somewhat less than the diameter actually employed, 3.71, whereby a reduction in velocity results but no a parent reduction in the heat-exchanging e ciency of the generator.

From the foregoing discussion of various embodiments of the invention and of various constructions for carrying out the novel process of the invention, it will be seen that the invention goes further than the conformance of the hydraulic mean depth with the total length of travel in a definite ratio of depth to length, even assuming that the depth has been chosen to give a desired high initial velocity which is substantially the extent of the prior art. In the embodiment of the invention shown in Figs. 5 to 7 inclusive, spacing ofthe gas-confining and heat-exch anging surfaces is varied from their lower to their upper ends to maintain a velocity of fluid flow over the generating tubes which will produce sufficient turbulence at the reduced temperatures to give the desired degree of heat-transferring force. This results in a variation of the hydraulic mean depth. In this embodiment of the invention, not only is the hyd aulic mean depth reduced at the outlet end, but the distribution of the generating tubes in the cross-sectional area of the passage at any point along its length is such that the cross-sectional area of the gas about each tube is substantially identical with that about any other tube.

It will be understood that the invention is not necessarily restricted to an arrangement of the heat exchanging surfaces with their greatest linear dimensions extending along the path of travel of the fluids but that other arrangements of these surfaces, including the varying spacing thereof, may be madethat will accomplish some or all of the objects of the invention.

What is claimed as new is: v

1. Apparatusfor the exchange of heat between a gas and a fluid comprising a wall defining a gas passage which tapers from one end toward the other, a set of closely spaced tubes of small diameter extending longitudinally from one end to the other of the passage, which are uniformly distributed throughout the entire cross-section of the passage anywhere in its length, said tubes being more closely spaced at the smaller end of the passage than the other and the dimensions and spacing of the tubes being such that the tubes have a surface area of at least 12 square feet per cubic foot of total volume of the passage whereby under a high velocity of gas flow marked turbulence in the gas is maintained, means for introducing heated gas into the wider end of the passage and means for introducing a. fluid into the tubes at the opposite end of the passage, and thereby causing the gas and fluid to flow in counter-flow relation.

2. 'Apparatus for the exchange of heat between a gas and a fluid comprising a wall de lining a gas passage which tapers from one end towards the other, a set of closely spaced tubes of small diameter extending longitudinally from one end to the other of the pas.- sage, which are uniformly distributed throughout the entire cross-section of the passage anywhere in its length, said tubes being more closely spaced at the smaller end of the passage than the other and the dimensions and spacing of the tubes being such that the tubes have a surface area of at least 12 square feet per cubic foot of total volume of the passage, and the taper of the passage being such that the velocity of the gas is reduced as it passes toward the outlet end but marked I turbulence in a gas flow of high velocity is maintained, means for introducing heated gas into the wider end of the passage and means for introducing a fluid into the tubes at the opposite end of the passage and thereby-causing the gas and fluid to flow incounterwater to said mechanical means, said tubes 1 being small in cross-section and more closely spaced at the narrow end of thepassage than at the other end, and, the dimensions and spacing of the tubes being such that the tubes have a surface area of at least 12 square feet per cubic foot of total volume of the passage, whereby under a high velocity of gas flow a marked turbulence in the gas is maintained, and means for introducing a heated gas into the wider end of the passage.

4:. A steam generator comprising walls forming a gas passage which tapers from one end toward the other, a set of closely spaced, substantially straight steam generating tubes extending lengthwise of the passage and constituting substantially the entire evaporating portion of the generator, said tubes having water inlet ends at the narrow end of the gas passage, mechanical means for introducing Water into the inlet ends of the tubes and means communicating with the other ends of the tubes for receivingthe generated steam and returning the unevaporated water to said mechanical means, said tubes being small in cross-section and more closely spaced at the narrow end of the passage than at the other end, and the dimensions and spacing of the tubes being such that the tubes have a surface area of at least 12 square feet per cubic foot of total volume of the passage, whereby under a high velocity of gas flow a marked tnrbnlence in the gas is maintained, and means for introducing a heated gas into the wider 

